R.Sale: Yes, you are right, I even felt a bit stupid posting this since it's such an insignificant pattern
But I still added it because things like this can help focus on the cultural background against which the VM sources were created. Not much is found in classical art, but I am finding more and more in "popular" art from the Greco-Roman period in Egypt. This is getting more specific, and would explain to some extent the art style of the figures. So it's not this pattern by itself, but in addition to other things I have posted from the same period.
The thought behind my posting these images is not necessarily that the patterns were invented by someone in that period. Little has been invented in ancient art. It's evolution, synthesis, adaptation, degeneration, refinement... of existing forms.
So when we see an artefact like this, we can assume that this was a way of drawing a certain material in Roman-Egyptian art made for the general public. So I add also little bits that point to this period, hoping that after a while enough pieces of the puzzle will be found to understand the precise cultural background of the original documents.
Of course, this implies that the 15th century copyists did not understand much of what exactly they were copying, apart from of course later additions like the crossbowman. But as the Carolingians show us, documents were sometimes just copied because of their antiquity, in order to preserve them.
It is interesting to learn what this pattern meant in heraldry. But was it usual to add a color to it, then? (green in this case) In Egypt, green meant fertility, rebirth, or young life - which would be appropriate given the young girl in this basket.